package com.test.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

public class CheckNumServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //如何让浏览器3秒自动刷新一次
        resp.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80, 20, BufferedImage.TYPE_INT_RGB);

        //得到图片
        Graphics2D graphics2D = (Graphics2D) image.getGraphics();

        //设置图片的背景颜色
        graphics2D.setColor(Color.white);
        graphics2D.fillRect(0,0,80,20);

        //给图片写数据
        graphics2D.setColor(Color.BLUE);
        graphics2D.setFont(new Font(null,Font.BOLD,20));
        graphics2D.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/png");

        //网站存在缓存，设置不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

        //把图片写给浏览器
        ImageIO.write(image,"png",resp.getOutputStream());


    }
    //生成随机数
    private String makeNum() {
        Random random = new Random();
        String num = random.nextInt(999999) + "";
        StringBuffer stringBuffer = new StringBuffer();
        for(int i = 0; i < 6 - num.length();i++){     //这段代码可以保证生成的验证码始终为6位
            stringBuffer.append("0");
        }
        num = stringBuffer.toString() + num;
        return num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}
